1. Field of the Invention
This disclosure relates to a fixing apparatus provided in an image forming apparatus on the basis of an electrophotographic system such as printers and copying machine.
2. Description of the Related Art
Examples of a fixing apparatus in practical use provided in an image forming apparatus on an electrophotographic system include a configuration having a cylindrical film, a heater configured to come into contact with an inner surface of the film, a backup member defining a nip portion together with the heater via the film. The fixing apparatus of this type is capable of fixing a toner image on a recording material by heating the recording material having a toner image thereon while conveying the recording material by the nip portion.
The fixing apparatus is known to be subjected to a phenomenon that the temperature of a non-sheet passing region rises when a recording material having a smaller width than a maximum conveyable size of the apparatus (hereinafter, referred to as a “small-sized sheet” is conveyed by the nip portion, so-called “temperature rise in the non-sheet passing portion”. Although an attempt is made to secure a long interval between a previous recording material and a following recording material in the case of a continuous printing in order to restrain the temperature rise in the non-sheet passing portion, there arises a problem that the productivity is lowered.
Accordingly, Japanese Patent Laid-Open No. 10-232576 discloses a fixing apparatus configured to restrain the temperature rise in the non-sheet passing portion without lowering the productivity by bringing an aluminum plate or the like into contact with a heater.
However, in the case where a thermal conduction member such as the aluminum plate is brought into contact with the heater over an entire area across a longitudinal direction like the configuration disclosed in Japanese Patent Laid-Open No. 10-232576, a temperature drop at end portions of the heater in the longitudinal direction may become prominent by heat movement and heat discharge accelerated at the end portions of the heater. Consequently, a fixation failure may occur at end portions in a widthwise direction when a maximum size recording material is passed.